The frequency of signals associated with integrated circuits (ICs), whether generated within the IC or exchanged with devices external to the IC, has steadily increased over time. As IC signals reach radio frequency (RF) ranges exceeding a gigahertz, it becomes viable to implement inductor structures within ICs. Implementing an inductor structure within an IC, as opposed to using an external inductor device, typically reduces the manufacturing and implementation costs of the system requiring the inductor. IC inductors can be implemented within a variety of RF circuits such as, for example, low noise amplifiers (LNAs), voltage controlled oscillators (VCOs), input or output matching structures, power amplifiers, and the like. Many of these RF circuits, such as certain VCO architectures, can be implemented as differential circuits that rely on circuit and/or device symmetry to provide maximum circuit performance.
Although IC inductors are advantageous in many respects, IC inductors introduce various non-idealities not present with external or discrete inductors. For example, an IC inductor is typically surrounded by other semiconductor devices that can generate noise. As IC devices reside over a common substrate material that is conductive, signals and noise generated by an IC device can be coupled into an IC inductor built over the common substrate material. Although IC inductors are typically built within one or more metal interconnect layers that reside farthest from the substrate layer, finite parasitic capacitances exist between the substrate layer and the metal interconnect layer(s). These parasitic capacitances can couple signals between the IC inductor and the substrate layer. Further, eddy currents induced within the substrate layer by an IC inductor can generate losses that reduce the quality factor, or so called “Q,” of the IC inductor.
Other non-idealities relate to the ability of interconnect lines routed in the vicinity of the IC inductor, particularly large ground and power supply lines, to couple signals both capacitively and inductively to the inductor. In addition, inductive coupling resulting from neighboring metal lines can alter the inductive value and self resonance of an IC inductor.
Each of the non-idealities described can interfere with the implementation of an IC inductor as a consistent and reproducible element whose parameters are independent of the IC environment within which the IC inductor resides.